Anthropologists have used the fossil record to construct tree-shaped diagrams that show how the different branches of hominins, which includes humans and human ancestors, split off from one another. These diagrams tend to proceed in a straight line, from the tree-trunk base of a common ancestor through progressively smaller branches until the species of interest is reached. The Neanderthal data suggests evolution did not proceed in a straight line. Rather, evolution appears to be a messier process, with emerging species merging back into the lines from which they diverged.
Now the view emerging from the genomic data suggests that Neanderthals who migrated out of Africa a few hundred thousand years ago re-encountered anatomically modern humans, who began migrating out of Africa some 80,000 years ago. Humans migrating out of Africa were likely to be small pioneering groups and appear to have encountered Neanderthals living in the Fertile Crescent of the Middle East about 60,000 years ago.
"It was a very unique series of events, with a founding population of modern humans of greatly reduced size -- tens to hundreds of individuals," Dr. Mullikin said. Geneticists can detect a population constriction or bottleneck where certain genetic markers are concentrated; that only occurs when the population is small.
"At that time," Dr. Mullikin continued, "where the population was greatly reduced, the modern humans migrating out of Africa encountered Neanderthals and inter-breeding occurred between the two groups, leaving an additional, but subtle, genetic signature in the out-of-Africa group of modern humans."<
|Contact: Larry Thompson|
NIH/National Human Genome Research Institute